An example of a motor-driven movement system for moving a movable element is a system comprising two actuators connected to the movable element and each dimensioned to be capable, on its own, of driving the movable element. The system also has a central control unit that is connected to the two actuators in order to send a position setpoint to each of the actuators. In operation, the central control unit sends a position setpoint to one of the actuators, referred to as a main actuator, which responds to the position setpoint by generating a force for moving the movable element. The second actuator, referred to as an emergency actuator, is not powered. In the event of the main actuator failing, the central control unit sends a position setpoint to the emergency actuator, which takes the place of the main actuator in order to move the movable element.
Nevertheless, since the lifetime of an actuator is directly linked to the forces it needs to develop, the main actuator wears quickly since, under normal operating conditions it is used on its own for driving the movable element. That is why provision may be made for each actuator to act in alternation as the main actuator and as the emergency actuator, but that complicates managing the operation of the actuators. It also remains necessary to dimension the actuators so as to be capable of developing the maximum force over very long periods, such that the actuators are relatively heavy and bulky.
Furthermore, under normal conditions of operation of the main actuator, the emergency actuator is inactive and thus generates a force on its connection to the movable element that tends to oppose the force developed by the main actuator for moving the movable element. The main actuator therefore needs to be dimensioned so as to be capable of overcoming this opposing force without consequence on the movement of the movable element.
Documents FR 2 908 107, US 2004/07500, ER 0 864 491, and WO 2007/002311 disclose motor-driven movement systems for moving movable elements, each system including two actuators, each of which is provided with means connecting it to the movable element. Each system includes a central control unit that, in a nominal situation, sends a control setpoint to one of the actuators such that said actuator acts alone to drive the movable element. In a situation that is more critical, e.g. in the event of turbulence opposing the movement of the movable element, the central control unit sends a control setpoint to each the actuators so that both actuators act simultaneously to drive the movable element. The use of only one or both actuators thus depends solely on the power needed to be able to drive the movable element.